idx/lib/idx.js.flow

Utility function for traversing properties on objects and arrays.

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 */

declare opaque type DeepRequiredArray<+T>: $ReadOnlyArray<
  DeepRequired<$NonMaybeType<T>>,
>;

declare opaque type DeepRequiredObject<+T: interface {}>: Required<{
  +[K in keyof T]: DeepRequired<T[K]>,
}>;

declare opaque type DeepRequired<T>: T extends empty
  ? $FlowFixMe // If something can pass empty, it's already unsafe
  : T extends $ReadOnlyArray<infer V>
  ? DeepRequiredArray<V>
  : T extends (...$ReadOnlyArray<empty>) => mixed
  ? T
  : T extends interface {}
  ? DeepRequiredObject<T>
  : $NonMaybeType<T>;

type UnboxDeepRequired<T> = T extends DeepRequired<infer V> ? V : T;

/**
 * @see https://github.com/facebook/idx
 *
 * If you entered the file with the hope to understand why something doesn't
 * type check, you should stop, and migrate your code away from idx first.
 * idx is deprecated, and you should always use optional chaining instead.
 */
declare module.exports: <T1, T2>(
  prop: T1,
  accessor: (prop: $NonMaybeType<DeepRequired<T1>>) => T2,
) => ?UnboxDeepRequired<T2>;